Conventional methods of producing heating, including burning fossil fuels and electric resistance heat generation, have disadvantages of increasing operating costs and, relatively, low energy efficiency. Heat pumps provide an improvement over these methods.
Heat pumps extract low temperature heat from some available source through evaporation of a working fluid at an evaporator, compress the working fluid vapor to higher pressures and temperatures and supply high temperature heat by condensing the working fluid vapor at a condenser. Residential heat pumps use working fluids such as R410A to provide air conditioning and heating to homes. High temperature heat pumps using either positive displacement or centrifugal compressors use various working fluids, such as HFC-134a, HFC-245fa and CFC-114, among others.
The choice of working fluid for a high temperature heat pump is limited by the highest condenser operating temperature required for the intended application and the resulting condenser pressure. The working fluid must be chemically stable at the highest system temperatures. The working fluid vapor pressure at the maximum condenser temperature must not exceed the feasible operating pressure of available compressors and heat exchangers. For subcritical operation, the working fluid critical temperature must exceed the maximum condenser operating temperature.
Increasing energy costs, global warming and other environmental impacts, in combination with the relatively low energy efficiency of heating systems that operate on fossil fuels and electrical resistance heating make heat pumps an attractive alternative technology. HFC-134a, HFC-245fa and CFC-114 have high global warming potential and CFC-114 also has a high ozone depletion potential. There is a need for low global warming potential, low ozone depletion potential working fluids for use in high temperature heat pumps. Fluids that enable operation of existing heat pump equipment designed for CFC-114 or HFC-245fa at higher condenser temperatures while still attaining an adequate heating capacity would be particularly advantageous.